Many components of a gas turbine engine must be supported in such a manner that they are retained in an axial direction of the engine and in the circumferential direction of the casing. For this purpose, in the centre casing area of a gas turbine engine outer carrier rings support nozzle guide vanes or stator vanes. A carrier ring itself is supported either by spokes, which also support the bearing and therefore the shaft of the engine and carry oil and buffer or sealing air to and from the bearing, or a structural diaphragm type component further downstream. Spokes and diaphragm are held in place by an outer casing.
During operation of the gas turbine engine, where a part of the compressor air flows by the spokes in order to cool transition ducts or to provide cooling for the nozzle guide vanes at the entry of the turbine section, poor air flow characteristics in the centre casing area of a gas turbine engine can cause dead areas behind the spokes, leading to low heat transfer coefficients on the outer carrier rings and on the inside surface of the outer casing.
Up to now the casing flow has been allowed to recirculate with low velocity with flow separations behind the spoke frame.